netdev - Re: Add a SOCK_DESTROY operation to close sockets from userspace

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Date:	Tue, 17 Nov 2015 19:27:38 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Lorenzo Colitti <lorenzo@...gle.com>
Cc:	netdev@...r.kernel.org, edumazet@...gle.com, ek@...gle.com,
	maze@...gle.com, dtor@...gle.com
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

On Wed, 18 Nov 2015 10:43:40 +0900
Lorenzo Colitti <lorenzo@...gle.com> wrote:

> This patch series adds the ability for a privileged process to
> destroy sockets belonging to other userspace processes via the
> sock_diag interface, and implements that for TCP sockets.
> 
> This functionality is needed on laptops and mobile hosts to
> ensure that network switches / disconnects do not result in
> applications being blocked for long periods of time (minutes) in
> read or connect calls on TCP sockets that will never succeed
> because the IP address they are bound to is gone. Closing the
> sockets in the protocol layer causes these calls to fail fast and
> allows applications to reconnect on another network.
> 
> For many years Android kernels have done this via an out-of-tree
> SIOCKILLADDR ioctl that is called when networks disconnect, but
> this solution is cleaner, more robust and more flexible. The
> system can iterate over all connections on the deleted IP address
> and close all of them. But it can also close all sockets opened
> by a given process on a given network, for example if the user
> has restricted that process from using that network, or if a
> secure network such as a VPN is now being applied to the
> application and thus previously-established connections are
> blackholed.
> 
> The patch series only implements SOCK_DESTROY for TCP sockets,
> but the mechanism can be extended to any protocol family that
> supports the sock_diag interface.
> 

I understand why you might want this, but it smells like the same
kind of problems that the "forced unmount" patch had which eventually
led to it not being accepted in mainline.  Lots of corner
cases and race conditions waiting to blow up.

Look at the issues that the multi-thread socket close has.
This looks worse.


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